Preheat the Oven: Preheat oven to 375°F (190°C). Line a 12-cup muffin pan with paper liners and lightly coat any exposed metal with cooking spray.
Prepare the Sugar Mix: In a separate small bowl, mix 1/2 cup (110 g) brown sugar with the cinnamon and chopped California Prunes.
Creaming butter and sugar: In the bowl of a stand mixer fitted with the paddle attachment, cream together the softened butter and granulated sugar on high speed until light and fluffy, about 2 minutes.
Incorporating wet ingredients: Add the eggs, Greek yogurt, applesauce, and vanilla extract to the bowl. Mix on medium-high speed until completely combined.
Combining dry ingredients: In a medium bowl, whisk together the flour, baking soda, baking powder, and salt. Gradually add the dry ingredients to the wet mixture, mixing on low speed until just combined.
Folding in the Prune + cinnamon mix: Gently fold about ¾ of the brown sugar and California Prune mixture into the batter by hand, folding only 3-4 times. Do not fully combine.
Fill the Muffin Pan: Spoon the batter into the prepared muffin pan, filling each well nearly to the top. Sprinkle the reserved prune and brown sugar mixture evenly over the tops of the muffins.
Baking: Bake for 20-22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Cool: Allow the muffins to cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.
Serve warm or at room temperature for a naturally sweet and wholesome treat!